Ministers and health officials urged people not to panic yesterday as police dealt with anthrax scares after suspect packets were discovered in Liverpool, London, and Scotland.

Buildings were evacuated, staff decontaminated and substances removed for analysis. No traces of anthrax had been found last night and the scares are likely to be confirmed as false alarms or hoaxes.

Scotland Yard urged the public to be alert. A spokeswoman said there was no intelligence of a "specific threat" to Britain of a biological or chemical attack.

The health secretary, Alan Milburn, told the Commons: "It is important that people remain calm and go about their normal lives."

Meanwhile the public health laboratory service confirmed that precautionary anthrax testing on three people in the UK has been completed. All three have tested negative.

In Liverpool, 400 post workers were evacuated from a sorting office in the city centre after a packet leaking white powder was discovered on the third floor.

More than 200 staff who could have come in contact with the parcel were isolated in a car park for seven hours as police and fire and ambulance crews investigated. Six postal workers were eventually escorted from the car park in protective suits to an ambulance service decontamination unit.

They were later taken to hospital for tests and given antibiotics. Test results on the powder should be available today.

Mark Rock, who was in the sorting office when the packet was found, said it had come from abroad, was destined for an address in the Toxteth area, and was at first treated as a joke.

"The bloke who was sorting it noticed the white powder leaking from it and started waving it in the air saying it was anthrax," he said. "But as he was waving it the powder came out."

In London, police investigated a suspect package sent to the offices of the Local Government Association in Smith Square, where government minister Nick Raynsford was meeting local government leaders.

A Scotland Yard spokeswoman said part of the building was evacuated and the package was removed and examined as a precautionary measure.

"We have no knowledge of anyone exhibiting ill effects," she added.

At the London stock exchange 12 workers were taken to hospital as a precautionary measure after a suspect package arrived in the mail room. "They were not suffering any ill effects and police are now investigating the matter," said a spokesman.

In Fife, police said that a number of packages "purporting to contain anthrax" had been delivered to various addresses, including St Andrews University, where Prince William is a student, and police headquarters in Glenrothes.

Fife's assistant chief constable, David Mellor, said: "There is every likelihood that these fall more into the hoax category that we have previously experienced here in Fife than any direct connection with other events currently ongoing elsewhere in the world."